Ruthenium, tris reductions

Tris(diimine)ruthenium(III) complexes are significantly more oxidizing than the analogous complexes of both iron(III) and osmium(III). This correlates well with the observation that rates of reduction in base are also faster for the tris(diimine)ruthenium(III) complexes. The tris(l,10-phenanthroline)ruthenium(III) reduction is significantly faster than the tris(2,2 -bipyridine)ruthenium(III) reduction, and this may be the reason why it is only the latter reaction that has been investigated in detail (1, 2). This system is particularly complex, and the rate law given by Eq. (1) holds only for very small concentrations of ruthenium complex. In contrast to the irondll) systems, simple kinetics... 

Newkome and coworkers also examined a dendritic system in which bipyridine molecules, incorporated into the branches, were subsequently complexed to yield dendrimers containing ruthenium tris-bipyridyl moieties dangling from the dendritic arms. In the electrochemistry of these compounds, the metal centers, surrounded by a dendritic network, exhibited irreversible kinetic behavior, as is commonly found in such systems. On the other hand, there are three separately identifiable ligand-based reductions, each of the... 

We now wish to test the above gel-reaction-diflfusion approach (Eqs 9.7-9.10) using the BZ reaction, which consists in the oxidation of malonic acid by bromate ions in acidic medium. The reaction proceeds only when catalyzed by a suitable metal ion. In the experiments, the chosen catalyst is the ruthenium tris(2,2 -bipyridine) that intervenes through its oxydo-reduction couple (Ru(bpy)3 /Ru(bpy)j ). In a batch reactor or a CSTR, this reaction exhibits well-documented periodic oscillations of concentrations in some region of the parameter space. 

Later, an improved system for C02 photofixation was reported by the same authors.164 The new system consisted of 6.5 x 1(T5 M tris(2,2 -bipyridine)ruthenium(II), Ru(bpy)3, as the photosensitive electron donor, methyl viologen (MV2+, 20 mM) as the electron acceptor, and triethanolamine (TEOA, 0.6 M) as a sacrificial electron donor in a C02-saturated aqueous solution (Fig. 18). Under irradiation with a 300-W high-pressure Hg lamp with a CuS04 chemical filter (A > 320 nm), formic acid, which was detected by isotachophoresis, was produced in quantum yields of ca. 0.01%. Recently, however, Kase et al.165 have repeated this experiment using a 13C02 tracer and have claimed that the formic acid obtained was produced not by C02 reduction but rather by oxidative cleavage of TEOA. 

Besides the electrochemical application, the (Cp )Rh(bpy)-complex 9 can also be used to reduce cofactors with hydrogen. In a recent study it was compared with ruthenium complex 13 [RuC12(TPPTS)2]2 (TPPTS tris(w-sulfonatophenyl)-phosphine Scheme 43.5). Both complexes were used to regenerate the cofactors in the reduction of 2-heptanone to (S)-2-heptanol, catalyzed by an ADH from Thermoanaerobium brockii (TfrADH) [46, 47]. The TON for both catalysts was 18. 

II. Rate Law and Stoichiometry for the Reduction of Dilute Solutions of Tris(diimine)iron(III)t -ruthenium(III), and -osmium(QI) in Base... 

The most widely studied and most exploited of inorganic ECL reactions, however, is that of tris(2,2 -bipyridine) ruthenium(II), [(bpy)3Ru]2+. The emissive excited state is a metal-to-ligand charge transfer state of triplet spin multiplicity the emission yield is approximately 10% and oxygen does not significantly quench the luminescence [22], The complex can exhibit ECL following sequential oxidation at the metal center and reduction of the coordinated 2,2 -... 

These chiral viologens were applied to the reduction of metmyoglobin, too [72]. In this reaction, the one-electron reduced viologen radical cations were photochemically produced by tris(2,2,-bipyridme)ruthenium(II) in the presence of disodium salt of ethylene diamine tetra acetic acid (Na2H2edta), and the cation radical reacts with metmyoglobin to reduce it. The (S,S) isomer more rapidly reacts with metmyoglobin than the (R,R) isomer. The reaction rate is analyzed with Michaelis-Menten mechanism, as shown in Scheme 29. 

Let us start with the complex in which the two ruthenium(III) tris(/3 -diketonate) centres are directly connected by an LL bridge with no spacer (R = R = CH3, (acac)2Ru(LL)Ru (acac)2 R = CH3, R = f-Bu, (dpm)2Ru(LL)Ru(dpm)2) " " . As illustrated in Figure 6, which refers to (acac)2Ru(LL)Ru(acac)2, such complexes undergo two stepwise oxidations and two stepwise reductions, all having features of chemical reversibility. The involved... 

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